This invention relates to a combined system that simplifies the required operations for shifting a manual transmission between speed ratios.
Heavy vehicles typically include a multi-speed transmission controlled by a manual stick shift. An engine drives the transmission through a selectively-actuated clutch. The operator selects one of several transmission speeds to result in various speed ratios between input from the engine and the output speed of the transmission.
In trucks there are typically ten or more different speed ratios available in a transmission. In shifting between the speed ratios, an operator may sometime sequentially pass rapidly through the several speeds. As an example an operator speeding up the vehicle may quickly pass through many of the gears in rapid succession.
The operation typically required to smoothly shift a truck transmission is relatively complex. Initially, a driver actuates the clutch to eliminate the torque transmission from the engine to the transmission. Transmissions are typically shifted between different speed ratios by sliding one toothed member relative to another. While torque is transmitted, there is a high torque load on the toothed members resisting any such movement. The clutch interrupts or breaks the torque transmission such that the operator is able to move the toothed members relative to each other. Thus, the driver actuates the clutch and moves the gears relative to each other to a neutral position. The driver then typically releases the clutch and attempts to synchronize the speed of the engine with the speed necessary at the next selected speed ratio to achieve a synchronous or smooth and continuous speed at the transmission output. That is, the driver attempts to achieve an engine input speed that matches the new speed ratio. If this does not occur, there is a "jerkiness" at the engagement of the new gear that is transmitted into uneven travel speed for the vehicle, and grinding of the transmission elements. A good deal of operator experience is required to even approximate synchronization of the speed ratio. If the driver cannot approximate the speed the shift cannot be completed. Moreover, the speed synchronization typically cannot be achieved identically and the operator again actuates the clutch as the new gear is being engaged. This multi-step method of shifting gears is relatively complex. Further it relies upon an experienced operator who has a feel for the desired speed at the next selected gear. As vehicles become equipped with additional controls for other driving operations, operators are required to perform more complicated operation steps. A typical truck driver today is also less experienced than in the past. These inexperienced operators will often lack sufficient experience for the speed synchronization and steps required to shift as described above.
The prior art has proposed systems that attempt to predict the engine speed that would be necessary at the next speed ratio and begin to move the engine speed to the desired speed to achieve speed synchronization. These systems have also proposed eliminating the need for actuating the clutch to move the transmission to neutral by measuring and attempting to achieve a zero torque speed for the engine. That is, there is an engine condition at which there is no torque transmitted to the transmission. At that condition, the operator will theoretically be able to move the gear out of engagement since no torque is holding the members in place.
These systems have typically been more "proposed" systems rather than practical production systems. One major failing of these systems is that it is difficult to identically measure or predict the zero torque condition or the synchronization speed. Also, the required torque meter would be expensive and difficult to maintain. Instead, both change with time. Moreover, the proposed systems generally assume that the engine control will always know what speed the transmission is in. In many of these systems, the operator is not provided with the ability to selectively use the clutch and complete a transmission shift manually as in the prior art. It is important to leave the operator with that option.
Also, the proposed prior art systems have not provided an operator with the ability to skip shift, or perform several shifts at once. The controls proposed in the prior art are not equipped to handle such a multiple shift and still synchronize speed.
There is also inadequate fault detection on the signals that an operator may send to the control. In any system that modifies the speed of the vehicle without operator control, it is most important to have fault detections on the signals that actuate the system. The prior art has not adequately provided fault detection.
In addition, the prior art has not proposed systems that will decelerate the engine rapidly when necessary. It is easier to rapidly increase the engine speed than to rapidly decrease the engine speed, as decreasing engine speed requires the elimination of rotational momentum. Full engine power is available to speed up, while friction must achieve most of the speed decrease. One cannot move engine fueling to a negative value.
Moreover, the proposed systems do not adequately allow for miscommunication between the operator and the control. A practical system must continue to monitor operator inputs during synchronization and assist the operator in shifting as necessary.
Finally, the prior art has not proposed a system that will have sufficient information relative to the current state of the transmission. A system should not modify engine speed until the transmission is in neutral. If the transmission is in gear and the engine control begins to increase the speed to synchronize the engine speed, the vehicle speed would increase unexpectedly. This would of course be undesirable. While recognizing this requirement, the prior art systems have not provided sufficient feedback and fail-safe monitoring of the state of the transmission.